408 s484 missing power over 15# boost
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In for a conclusion on this... I am surprised it taps out so soon if its a backpressure issue. Running that exact turbo on a 9:1 5.3 with 317s I get great gains all the way up to 30psi. It’s not until that 30+ mark that it’s not making much power. 30 is good for 1025whp and 35psi only makes 1088whp. The happy spot on my combo seems to be that 26-28psi range. Just some data points, now I’ll pay attention to what you guys find.
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i can crank the dwell up abound 4+ms if you think that may help
Try to tighten the gap to .015. Others have had to go that tight to keep the spark from blowing out. Should rule out the spark blow out theory anyway. Then you can move on to other possibilities.
Seems pretty random with who does/doesn’t have spark issues. Many of the Holley guys with spark issues around the OP’s power level seemed to be able to bypass the issues with a really short gap. It’s worth a shot being free and easy to do anyway. Most don’t gap down far enough to trouble shoot blowout IMO. .015 or smaller to test.
Were you on E85? I think there’s a ton more fuel in the cylinder and you need more spark in general. Also wonder if guys are cooling the ethanol down too much with the bad *** intercoolers. “Cool” ethanol is harder to ignite. I know a few of the guys that race target 150+ degrees because the fuel supposedly burns better. (not saying there’s any merit to it, but it makes sense). Pretty sure Mark F. ran the crappo Ebay IC and had pretty high charge temps.
Last edited by Forcefed86; Nov 16, 2017 at 12:50 PM.
In for a conclusion on this... I am surprised it taps out so soon if its a backpressure issue. Running that exact turbo on a 9:1 5.3 with 317s I get great gains all the way up to 30psi. It’s not until that 30+ mark that it’s not making much power. 30 is good for 1025whp and 35psi only makes 1088whp. The happy spot on my combo seems to be that 26-28psi range. Just some data points, now I’ll pay attention to what you guys find.
i just finished a foxbody with SBE 5.3 and S484 with 1.58AR. Made 750whp on 16psi, 11.8afr and 1040whp on 25psi 11.6afr. Compression is 9.6:1 with a 226/235 BTR cam and spinnning 7800rpm. Holley dominator with Br7efs gapped at 0.024 running Metco coils. 4.5ms dwell. Shows no issues of running out anytime soon.
http://pix.sfly.com/_PNf1Zhd
http://pix.sfly.com/_PNf1Zhd
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Joined: May 2011
Posts: 560
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I agree, I just dont know how much. I’d think the turbo could hang in there till at least low 20s before it started choking out like that tho... or does the added size really change things THAT drastically?
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Certainly is, but we’ve gone mid 8’s at high 150’s in a 3700lb car with a 76mm borg and a 408 at much higher boost then the OP is running. Granted Jose said we spun the **** out of it, shaft was blue. It still made 950 through a 400 and 28” tire.
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it is a martin smallwood specced cam motion cam. i dont recall exactly the numbers. low 230s at .050" .600 lift with wide lobe sep.
i am at home and all that is at my shop.
i am at home and all that is at my shop.
Last edited by fastbarry; Nov 17, 2017 at 09:06 AM.
Thread Starter
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i built a 408 primarily for a wide power curve for offroad use and still do 1000 hp.
i find it hard to believe i am over flowing the turbo at this point. i will try to get it back on the dyno this weekend and close the plug gap
i find it hard to believe i am over flowing the turbo at this point. i will try to get it back on the dyno this weekend and close the plug gap
i just finished a foxbody with SBE 5.3 and S484 with 1.58AR. Made 750whp on 16psi, 11.8afr and 1040whp on 25psi 11.6afr. Compression is 9.6:1 with a 226/235 BTR cam and spinnning 7800rpm. Holley dominator with Br7efs gapped at 0.024 running Metco coils. 4.5ms dwell. Shows no issues of running out anytime soon.
http://pix.sfly.com/_PNf1Zhd
http://pix.sfly.com/_PNf1Zhd
i just finished a foxbody with SBE 5.3 and S484 with 1.58AR. Made 750whp on 16psi, 11.8afr and 1040whp on 25psi 11.6afr. Compression is 9.6:1 with a 226/235 BTR cam and spinnning 7800rpm. Holley dominator with Br7efs gapped at 0.024 running Metco coils. 4.5ms dwell. Shows no issues of running out anytime soon.
http://pix.sfly.com/_PNf1Zhd
http://pix.sfly.com/_PNf1Zhd
Fwiw, Ablakez28 ran a s484 with a 408. I believe had ls3 heads on home built turbo kit(that i bought). He clicked off 8.85 at 150+mph. I think it was 20-21psi. Prior to that, stock 6.0l n s480 made 888/1004, ran 9.0s